| Description: |
Deficiency of the ADAMTS 13 protease, which cleaves von Willebrand factor, is associated with an increased risk of thrombotic thrombocytopenic purpura (TTP). Deficiency of this protease may be congenital, or more commonly due to an autoantibody (inhibitor). Hemolytic-uremic syndrome (HUS) is a thrombotic microangiopathy more commonly seen in children and associated with exposure to enterotoxigenic E. coli serotype 0157:H7. TTP and HUS have similar presentations and can be challenging to distinguish. Both present with microangiopathic changes on the peripheral smear, and may be associated with fever, renal failure, and CNS dysfunction. TTP/HUS is a clinical diagnosis; treatment should not be delayed while awaiting laboratory confirmation. Severe deficiency of ADAMTS 13 (<5%) in the appropriate clinical context supports a diagnosis of TTP. However, moderate to severe deficiency of ADAMTS 13 has been observed in a variety of other conditions, including sepsis and DIC. In addition, some patients with idiopathic TTP/HUS have normal or only moderately decreased ADAMTS 13 levels, consistent with alternate disease mechanisms with a common clinical phenotype. Determination of ADAMTS-13 activity has prognostic value; relapses are less common in patients without severe deficiency. The presence of an inhibitory ADAMTS-13 autoantibody may suggest response to immunosuppressive therapy (e.g, steroids or rituxumab). ADAMTS-13 testing at Stanford includes determination of ADAMTS-13 activity, and whether an autoantibody is present. |
